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overvoltage on audio circuits



 
 
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  #21  
Old October 30th 19, 05:01 PM posted to rec.audio.pro
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Default overvoltage on audio circuits

On Wed, 30 Oct 2019 13:58:13 +0000 (UTC), Ralph Barone > wrote:

> wrote:
>> On 29 Oct 2019 11:28:57 -0400, (Scott Dorsey) wrote:
>>
>>> geoff > wrote:
>>>> On 29/10/2019 8:04 am, gareth magennis wrote:


>>
>> This mechanism exists in all electrical conductors, but is only an issue
>> in microcircuits because the
>> conducting lines are so small and the current densities are therefore very high.
>>

>
>I was under the impression that electromigration was only an issue in
>modern microprocessors and other ICs built using nanometer scale
>transistors. I would assume that an op amp is built with huge transistors
>(and huge traces) in order to achieve low noise, and would therefore be
>relatively immune to electromigration damage.


Nope, electromigration has always been a concern and is one of the two most important reliability
issues in layouts. The other being electrostatic discharge. Huge traces is a relative term, microcircuits
are tiny.

Besides, large interconnect traces result in large parasitic capacitances which have a major impact on
AC charateristics (phase margin, BW, etc.), not to mention the impact on chip size and therefore
chip cost. Also, bipolar amps don't use large devices to reduce noise.
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  #22  
Old October 31st 19, 04:33 AM posted to rec.audio.pro
Phil Allison[_4_]
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Posts: 457
Default overvoltage on audio circuits

wrote:

--------------------


> Also, bipolar amps don't use large devices to reduce noise.



** Discrete op-amps use paralleled BJTs at the inputs and fairly high current levels to get voltage noise down low as possible.

Enlighten us -

what magic trick do integrated ones use instead ?



.... Phil

  #23  
Old October 31st 19, 03:08 PM posted to rec.audio.pro
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Default overvoltage on audio circuits

On Wed, 30 Oct 2019 20:33:11 -0700 (PDT), Phil Allison > wrote:

wrote:
>
>--------------------
>
>
>> Also, bipolar amps don't use large devices to reduce noise.

>
>
>** Discrete op-amps use paralleled BJTs at the inputs and fairly high current levels to get voltage noise down low as possible.
>
>Enlighten us -
>
>what magic trick do integrated ones use instead ?
>


Without getting too wordy, main components of bipolar noise are shot noise, which is a noise in the collector current and goes as the sq rt of emitter
bias current, the thermal resistor noise of all resistance at the base of the signal input bipolar devices, and the IR voltage noise developed at the
base by the shot noise divided by transistor beta times base resistor value. Increasing bias currrent increases shot current noise at the collector
and base, so low noise bipolar amps tend to be biased at lower currents. Base resistance is a function of the area and the length of the current path.
Since the depth of the resistor path in an IC is fixed by the fab process, one way the area and length are optimized is by using long, skinny min
width emitters with base contacts the same length as the long emitters and on both sides on the emitters. Usually the device will have multiple long
emitter stripes so that each long base contact in between the emitter stripes serve both emitters on each side, reducing base resistance by 2. True, a
larger device could continue to reduce base resistance, but other performance parameters must be met so base resistance is minimized by transister
geometry rather than brute force size. Not sure why discreet amps would use high currents for low noise. Shot noise is independent of process and
increases with current. Perhaps they practically eliminated all base resistance so there is no thermal or base shot noise component. They woud still
have the collector shot noise to deal with.Possibly they dealt with it with more transistors and more power eslehwere in the design. Don't know. ICs
don't have the luxery of having the unlimited power and cost available to high quality hifi stuff. Of course, amp designs with high power output
drive must use large transistors and high bias currents, perhaps this requirement reflects through the entire design.

I designed a decent low noise op amp a few years ago, the OPA1662, 3.3nv/rtHz noise densisty. -124db distortion, total noise+distortion 0.00006%,
22MHz GBW, 22V/uS SR, Sig/noise 95db, voltage gain 114db, and ..... 1.5ma power draw total.


  #24  
Old October 31st 19, 09:42 PM posted to rec.audio.pro
geoff
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Posts: 1,546
Default overvoltage on audio circuits

On 1/11/2019 3:08 am, wrote:
> On Wed, 30 Oct 2019 20:33:11 -0700 (PDT), Phil Allison > wrote:
>
>> wrote:
>>
>> --------------------
>>
>>
>>> Also, bipolar amps don't use large devices to reduce noise.

>>
>>
>> ** Discrete op-amps use paralleled BJTs at the inputs and fairly high current levels to get voltage noise down low as possible.
>>
>> Enlighten us -
>>
>> what magic trick do integrated ones use instead ?
>>

>
> Without getting too wordy, main components of bipolar noise are shot noise, which is a noise in the collector current and goes as the sq rt of emitter
> bias current, the thermal resistor noise of all resistance at the base of the signal input bipolar devices, and the IR voltage noise developed at the
> base by the shot noise divided by transistor beta times base resistor value. Increasing bias currrent increases shot current noise at the collector
> and base, so low noise bipolar amps tend to be biased at lower currents. Base resistance is a function of the area and the length of the current path.
> Since the depth of the resistor path in an IC is fixed by the fab process, one way the area and length are optimized is by using long, skinny min
> width emitters with base contacts the same length as the long emitters and on both sides on the emitters. Usually the device will have multiple long
> emitter stripes so that each long base contact in between the emitter stripes serve both emitters on each side, reducing base resistance by 2. True, a
> larger device could continue to reduce base resistance, but other performance parameters must be met so base resistance is minimized by transister
> geometry rather than brute force size. Not sure why discreet amps would use high currents for low noise. Shot noise is independent of process and
> increases with current. Perhaps they practically eliminated all base resistance so there is no thermal or base shot noise component. They woud still
> have the collector shot noise to deal with.Possibly they dealt with it with more transistors and more power eslehwere in the design. Don't know. ICs
> don't have the luxery of having the unlimited power and cost available to high quality hifi stuff. Of course, amp designs with high power output
> drive must use large transistors and high bias currents, perhaps this requirement reflects through the entire design.
>
> I designed a decent low noise op amp a few years ago, the OPA1662, 3.3nv/rtHz noise densisty. -124db distortion, total noise+distortion 0.00006%,
> 22MHz GBW, 22V/uS SR, Sig/noise 95db, voltage gain 114db, and ..... 1.5ma power draw total.
>
>


Is that better than a 741 ? ;- )

geoff
  #25  
Old November 1st 19, 11:02 PM posted to rec.audio.pro
Phil Allison[_4_]
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Posts: 457
Default overvoltage on audio circuits

wrote:

--------------------

>
> >> Also, bipolar amps don't use large devices to reduce noise.

> >
> >
> >** Discrete op-amps use paralleled BJTs at the inputs and
> > fairly high current levels to get voltage noise down low as possible.
> >
> >Enlighten us -
> >
> >what magic trick do integrated ones use instead ?
> >

>

--------------------------------------------------
>
> Increasing bias currrent increases shot current noise at the collector
> and base, so low noise bipolar amps tend to be biased at lower currents.



** FYI so called "shot noise" is not relevant to input devices operating over the full audio band. High frequency noise completely dominates.


> Not sure why discreet amps would use high currents for low noise.



** Then you are simply not very familiar with audio circuitry - as I suspected.

The idea is to get the best NF impedances down to around 150ohms for use with dynamic mics.


> I designed a decent low noise op amp a few years ago, the OPA1662, 3.3nv/rtHz noise densisty. -124db distortion, total noise+distortion 0.00006%,
> 22MHz GBW, 22V/uS SR, Sig/noise 95db, voltage gain 114db, and ..... 1.5ma power draw total.



** Nice part - but with about 1uV of input noise.

With 3.3nV and 1pA per rtHz of input noise, the best impedance is 3.3kohms.

Though obsolete, this op-amp set a bench mark for low noise audio.

https://www.analog.com/media/en/tech...016SSM2017.pdf

Note the fairly high supply current.


...... Phil

  #26  
Old November 2nd 19, 08:25 PM posted to rec.audio.pro
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Posts: 16
Default overvoltage on audio circuits

On Fri, 1 Nov 2019 15:02:56 -0700 (PDT), Phil Allison > wrote:

>>

>--------------------------------------------------
>>
>> Increasing bias currrent increases shot current noise at the collector
>> and base, so low noise bipolar amps tend to be biased at lower currents.

>
>** FYI so called "shot noise" is not relevant to input devices operating over the full audio band. High frequency noise completely dominates.


That's a surprise to me and many others as well, since shot noise is white noise and broadband, extending orders of magnitude beyond the audio range.
What is this "high frequensy noise" if it is not shot wde band noise or thermal wide band noise?
>
>> Not sure why discreet amps would use high currents for low noise.

>
>The idea is to get the best NF impedances down to around 150ohms for use with dynamic mics.


What do you mean here by NF? Are you referring to noise factor or noise figure? Those are ratios, not impedances. NF in my world is the SNRout/SNRin,
it's a measure of extra noise to the signal added by a component. Matching impedances gets maximum power to the load, but that is not what is desired
here. A microphone generates a small voltage and can tolerate very little current draw without distorting. The object is to amplify the microphone
VOLTAGE without loading it, not maximize power delivered to the amp. The last thing you want to do is put 150 ohm load on the microphone input. BTW,
the YBM data sheet gives the diff input impedance as 1Mohm or higher, depending on gain setting, which is what I would expect.
>
>> I designed a decent low noise op amp a few years ago, the OPA1662, 3.3nv/rtHz noise densisty. -124db distortion, total noise+distortion 0.00006%,
>> 22MHz GBW, 22V/uS SR, Sig/noise 95db, voltage gain 114db, and ..... 1.5ma power draw total.

>
>** Nice part - but with about 1uV of input noise.
>With 3.3nV and 1pA per rtHz of input noise, the best impedance is 3.3kohms.


How are you coming up with these numbers? They certainly do not agree with either the design results, application characterization, or with the
feedback from customers. Did you get them by dividing the input voltage noise density by the input current noise density? If so, what do you think
that gives you?
>
>Though obsolete, this op-amp set a bench mark for low noise audio.
>
>https://www.analog.com/media/en/tech...016SSM2017.pdf
>


Well let's compare your "benchmark" with the OPA1662. Conditions do not perfectly match, but I've gotten them close.

YBM OPA1662

Total Harmonic noise distortion 0.008 0.00006 % conditions
input voltage noise density 107 3.3 nv/rtHz 1KHz, G=1
" 12 2.9 " G=10
" 2 2.7 " G=100
" 1 2.6 " G=1000
input noise current density 2 1 pa/rtHz 1KHz input bias current
25 1.2 ua wc
input voltage noise density corner (1/f noise) 70 8 Hz
THD+ noise 0.007 0.0005 % G=2, [RL=5K YBM, 2K OPA]
Slew rate 17 22 V/uS
sm sig bandwidth 4 20 MHz G=1
Ips 10.6 1.5 ma

Now lets calculate input noise value using the YBM data sheet procedure and comparing to the YBM results -
From the YBM data sheet --------
For a microphone preamplifier, using a typical microphone im-pedance of 150 ohms, from the YBM data sheet,
using En =sqrt {(1 nVvHz)2 + 2 (pA/vHz× 150 ohms)2 + (1.6 nV/vHz)2} we get the input noise as

YBM OPA1662
noise source en = (for G=1,10,100,1000) 107,12,2,1 3.3,2.9,2.7.2.6
in = 2 1 pa/rtHz
RS = 150 ohm, microphone source impedance 1.6 1.6 nv/rtHz
et = 1.6 nV/[email protected] 1 kHz, microphone thermal noise
for G=1000 1.93 3.0 nv/rtHz
and for G=100 2.65 3.1 "
and for G=10 12 3.2 " and for
G=1 108 3.3 "

>Note the fairly high supply current.


Indeed, but I don't think it has anything to do with low noise, in fact, the noise is actually quite hign for except for very high gain settings. The
fact that it goes down so rapidly at high gain settings has very little to do with bias currents and says that the noise gain loop has been tweaked.
Noise gain is usually tweaked in the customer application to give the user more flexibility since it can impact other parameters, but is often tweaked
in the circuit as well. Having an order of magnitude reduced amplifier BW also reduces noise.
>
>** Then you are simply not very familiar with audio circuitry - as I suspected.


Let me say a little about that. I have designed audio circuits for 30 years. One was selected by Electronics Design magazine as Product of the Year. I
have presented papers at the International Solid States Conference in NYC. I have 25 patents as individual inventor, not global group co-inventer as
some places do. My designs are in avionics, satellites, medical equipment, and one is currently in every battery powered Apple product. However, I
will bow to an obviously superior master. Please tell me about your honors and designs and explain why my unworthy OPA1662 seems to be purchased in
the millions by these equally clueless customers such as Shure, Pioneer, and Marantz.

You know what I think? I've noticed in past posts when someone posts seeking help, and they've misunderstood their application or made a mistake,
rather than offering assistance, you call them an idiot. People like that are usually the C students in college and have limited accomplishments at
work, and use forums like this to bully those who know even less. Here, rather than offering transistor theory to prove your point, you pull out an
old data sheet designed by someone else and say, "see, see, it has high currents and low noise" without any understanding of the circuit. I would have
been impressed if you had offered theory and knowledge new to me, but didn't happen.

So, once again, please tell me how you came up with 3.3Kohms as input impedance for the OPA1662. The only resistance of the amp that affects noise is
the actual parasitic resitance of the base diffusion resistor of the input bipolar transistor, which is about 20 ohms. The dynamic input impedance is
set by the AC path, doesn't affect noise, and is not calculated by dividing the input voltage noise density by the input current noise density, if
that's what you did, then shows an appalling lack of understanding. Also, explain to me the mechanism of how the high current levels of YBM reduced
the noise. Also explain why, at 14% of the current draw, the OPA eq input noise bests in a major way or matches YBM for all gain settings below 100.
While you're at it, explain why you appear to want a 150 ohm NF input resistance for the amp.



>..... Phil
>

  #27  
Old November 3rd 19, 12:28 AM posted to rec.audio.pro
Phil Allison[_4_]
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Posts: 457
Default overvoltage on audio circuits

wrote:

-------------------
>
>
> >** FYI so called "shot noise" is not relevant to input devices operating
> > over the full audio band. High frequency noise completely dominates.

>
>
> That's a surprise to me and many others as well, since shot noise is white noise and broadband, extending orders of magnitude beyond the audio range.
> What is this "high frequensy noise" if it is not shot wde band noise or thermal wide band noise?
> >



** Whatever name you give it, the noise is essentially white and so rises with frequency being proportional sq.rt of the bandwidth.


> >> Not sure why discreet amps would use high currents for low noise.

> >
> >The idea is to get the best NF impedances down to around 150ohms for use with dynamic mics.

>
> What do you mean here by NF?


** Noise Figure.

> Those are ratios, not impedances.


** BJTs have noise figures in dBs that vary with the source resistance and current. There are optimum values for both giving the lowest NF.

Surely you have seen the curves published on data sheets.



> A microphone generates a small voltage and can tolerate very little
> current draw without distorting.


** Dynamic mics can deliver signals of a volt or so while condenser types output several volts.

Dynamic mics have a source impedance that is mostly restive and a typically couple of hundred ohms. The load needs to be a few times higher for best results.

A good mic pre-amp needs to have input voltage noise less then that of a 200ohm resistor when operating at high gain, like 1000 times.



> >> I designed a decent low noise op amp a few years ago, the OPA1662, 3.3nv/rtHz noise densisty. -124db distortion, total noise+distortion 0.00006%,
> >> 22MHz GBW, 22V/uS SR, Sig/noise 95db, voltage gain 114db, and ..... 1.5ma power draw total.

> >
> >** Nice part - but with about 1uV of input noise.
> >With 3.3nV and 1pA per rtHz of input noise, the best impedance is 3.3kohms.

>
> How are you coming up with these numbers?
>


** You are asking some very strange things.

> They certainly do not agree with either the design results,
> application characterization, or with the feedback from customers.



** There is no disagreement with the published data, at all.


> Did you get them by dividing the input voltage noise density by the input current noise density? If so, what do you think that gives you?


** It gives you a good guide to the source resistance that gives the best NF.

Do the same for a JFET op-amp and you get about 1Mohm, cos the current is so low. 1uV of noise in the audio band is many times that of a 200ohm resistor.

Is that news to you ?


> >Though obsolete, this op-amp set a bench mark for low noise audio.
> >
> >https://www.analog.com/media/en/tech...016SSM2017.pdf
> >

>
> Well let's compare your "benchmark" with the OPA1662.
>



** The SSM part beats it easily cos it is actually dedicated mic pre-amp, with a single resistor for gain control.

Did you not read the heading on the data sheet ?

You would need three op-amps connected as an instrumentation amplifier to do the same job and it would then behave like the SSM with input noise increasing at lower gains.


> >Note the fairly high supply current.

>
>
> Indeed, but I don't think it has anything to do with low noise, in fact, the noise is actually quite hign for except for very high gain settings.


** Got news for you pal.

Having very low input noise only matters at high gain settings cos one adjusts the gain setting to get an output of about 1Vrms.

So the actual input signal is about 1mV at high gain and proportionally more at lower gains, defeating any input noise increases going on.


> The fact that it goes down so rapidly at high gain settings has very little to do with bias currents and says that the noise gain loop has been tweaked.



** The common mode resistor that sets the gain ADDS to the input noise.

Unavoidable with that topology and not important in practice.

YOU are simply not very familiar with audio circuitry - as I suspected.



> Let me say a little about that. I have designed audio circuits for 30 years.
>


** Makes you familiar only with your own designs.

Those which you have not seen remain a complete mystery.



One was selected by Electronics Design magazine as Product of the Year. I
> have presented papers at the International Solid States Conference in NYC. I have 25 patents as individual inventor, not global group co-inventer as
> some places do. My designs are in avionics,



** FFS - that is more than enough solo trumpet playing.

Mics and mic pre-amps are not your thing.

If you have not spent many years dealing with them, like I have, you are not going to know very much about them.


> Please tell me about your honors and designs and explain why my
> unworthy OPA1662 .........


** Where did I say anything like that ???

I said it was a "nice part", but with 1uV of input noise in the audio band.


> You know what I think?



** Not very interested, thanks.

Because you are now beginning to sound like a raving lunatic.

Why are you posting on a pro-audio usenet group at all ??

BTW:

I use my real name and identity here, while you do not.

Attacking me from a position of anonymity is cowardly in the extreme.


( rest of this pig's misconstrued and paranoid garbage snipped )




...... Phil
  #28  
Old November 4th 19, 08:11 PM posted to rec.audio.pro
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Posts: 16
Default overvoltage on audio circuits

On Sat, 2 Nov 2019 16:28:47 -0700 (PDT), Phil Allison > wrote:

wrote:


>> >** FYI so called "shot noise" is not relevant to input devices operating
>> > over the full audio band. High frequency noise completely dominates.


>> That's a surprise to me and many others as well, since shot noise is white noise and broadband, extending orders of magnitude beyond the audio range.
>> What is this "high frequensy noise" if it is not shot wde band noise or thermal wide band noise?


>** Whatever name you give it, the noise is essentially white and so rises with frequency being proportional sq.rt of the bandwidth.


Since you are an audio expert, I am surprised that you did not know ----

That shot noise is white noise
That the " High frequency noise that completely dominates" is known as thermal or Johnson noise
That either shot or thermal noise or both can be important noise sources depending on the application. Just because shot noise is not a factor in
your microphone case does not mean it's never important.

>> >> Not sure why discreet amps would use high currents for low noise.


>> >The idea is to get the best NF impedances down to around 150ohms for use with dynamic mics.


The dominant noise source in this app is the parasitic base resistance of the input biplor and is not a function of bias current.

>> A microphone generates a small voltage and can tolerate very little
>> current draw without distorting.


>** Dynamic mics can deliver signals of a volt or so while condenser types output several volts.


I'm sure you know that you want the diaphram to move as little as possible to keep the response as linear as possible and thus distortion low, thus it
will be putting out a small volatge.

> >> I designed a decent low noise op amp a few years ago, the OPA1662


>> >** Nice part - but with about 1uV of input noise.
>> >With 3.3nV and 1pA per rtHz of input noise, the best impedance is 3.3kohms.


>> How are you coming up with these numbers?
>> Did you get them by dividing the input voltage noise density by the input current noise density? If so, what do you think that gives you?


>** It gives you a good guide to the source resistance that gives the best NF.
>Is that news to you ?


Yes it is. I've never known anyone to do that before, let alone think it means anything. I could put a Darlington on the inputs, get the shot noise
down 0.005na/rtHz. Would you then come up with 3.3Mohms as meaning something?

>> >Though obsolete, this op-amp set a bench mark for low noise audio.


>> >https://www.analog.com/media/en/tech...016SSM2017.pdf


> >Note the fairly high supply current.


I'm glad we're back on point. I originally said that high currents and large devices were not needed for low noise in bipolars. You said I was wrong
and pointed to the SSM as proof. I suppose "high currents" and "large devices" are relative terms, so I'll say more. Shot noise increases with current
and is independent of manufacturing process and device size, period. Thermal noise is dominated in a bipolar by the parasitic resistance in the base
of the input device. Even with best layout geometry, the resistance can always be made smaller by increasing the emitter width (larger device).
However, in the 40V analog processes I'm familiar with, and all 40V processes will have similar resistivities to get the breakdown voltages, a bipolar
with a 1nv/rtHz thermal noise can be designed with dimensions about 200u x 200u. This is not a minimum size device by any means, but it's not exactly
huge, on the OPA design two of these devices together would take up 15% of the chip area, and it's a small chip. Had this size been used, the OPA
would have a 1nv/rtHz noise density spec. However, our customers told us 3nv/rtHz was quite adequate and they preferred lower Ips, better distortion,
and better AC. The OPA comes in a dual, and each amp uses 45mW, far lower than competing devices with similar specs. I suppose very old manufacturing
processes would have larger feature sizes, but even 15 or 20 year old processes wouldn't give monstrous devices.

> YOU are simply not very familiar with audio circuitry - as I suspected.


>> Let me say a little about that. I have designed audio circuits for 30 years.


>** FFS - that is more than enough solo trumpet playing.


I very, very rarely do that, and I could have said much more. I did so in this case to show the absurdity of your repeateded statements that I knew
nothing about audio. I don't feel the need to broadcast anything. My plaques and patents are in boxes, and my walls instead have posters. I also don't
feel the need to belittle anyone or call them an idiot.

>> Please tell me about your honors and designs and explain why my
>> unworthy OPA1662 .........


>** Where did I say anything like that ???


>I said it was a "nice part", but with 1uV of input noise in the audio band.


For the OPA I get 0.49uV input noise over the audio band, for the SSM I get 0.27uV. Both of these numbers give excellent S/N ratios, and it is likely
the better distortion of the OPA compensates for the extra noise so that the signal error of each is close. Be that as it may, the OPA was not
designed as a special purpose amp for this application, it is a general purpose op amp. Nevertheless, Shure buys it as a microphone amp for battery
powered applications.

> BTW:
> I use my real name and identity here, while you do not.
> Attacking me from a position of anonymity is cowardly in the extreme.


And I won't. I am under a non-dosclosure agreement. I probably said more than I'm supposed to already, I sure as hell am not going to have someone see
my name in a newsgroup and report that I am blabbing away secrets. Anyway, I could list any name and how would you know if it was real or not?

As far as "attacking" you goes, I said you had an attitude and often called past posters idiots when they were looking for help. You have several
times told me I know nothing about audio. I question what drives someone to be like that.
  #29  
Old November 4th 19, 11:44 PM posted to rec.audio.pro
Phil Allison[_4_]
external usenet poster
 
Posts: 457
Default overvoltage on audio circuits

wrote:

---------------------

**This raving nutter needs dealing with.

>
> >** Whatever name you give it, the noise is essentially white and

> so rises with frequency being proportional sq.rt of the bandwidth.
>
> Since you are an audio expert,



** I am, and you are very clearly not.



> >> A microphone generates a small voltage and can tolerate very little
> >> current draw without distorting.

>
> >** Dynamic mics can deliver signals of a volt or so while condenser
> > types output several volts.

>
> I'm sure you know that you want the diaphram to move as little as possible
> to keep the response as linear as possible and thus distortion low, thus it
> will be putting out a small volatge.
>


** Absurd drivel.

You know less than nothing about microphones in actual use.



> >** It gives you a good guide to the source resistance that gives
>> the best NF. Is that news to you ?

>
> Yes it is. I've never known anyone to do that before,



** Proves you have no real understanding of input noise.

Just a plie of rote learned irrelevances.



>
> >> Let me say a little about that. I have designed audio circuits for 30 years.

>
> >** FFS - that is more than enough solo trumpet playing.

>
> I very, very rarely do that,


** But are just about to do it again.

How sickening.


> > BTW:
> > I use my real name and identity here, while you do not.
> > Attacking me from a position of anonymity is cowardly in the extreme.

>
> And I won't. I am under a non-dosclosure agreement.


** But see no obligation to NOT post wild bull**** on public forums ?

How fascinating.


> As far as "attacking" you goes, I said you had an attitude and often
> called past posters idiots when they were looking for help.


** And you're real sure they were not all idiots ?

How would YOU know that?

I doubt you have any way to tell.


....... Phil

  #30  
Old November 5th 19, 10:43 PM posted to rec.audio.pro
[email protected]
external usenet poster
 
Posts: 16
Default overvoltage on audio circuits

On Mon, 4 Nov 2019 14:44:22 -0800 (PST), Phil Allison > wrote:

> wrote:
>
>---------------------
>
>**This raving nutter needs dealing with.
>>
>> Since you are an audio expert,


>** I am, and you are very clearly not.


OK,, let's look at one of the few pearls of wisdom where you attempted to actually provide supporting calculations for one of your statements

YOU
>> >With 3.3nV and 1pA per rtHz of input noise, the best impedance is 3.3kohms.


ME
>> How are you coming up with these numbers?
>> Did you get them by dividing the input voltage noise density by the input current noise density? If so, what do you think that gives you?


YOU
>** It gives you a good guide to the source resistance that gives the best NF.
>Is that news to you ?


ME
>Yes it is. I've never known anyone to do that before, let alone think it means anything. I could put a Darlington on the inputs, get the shot noise
>down 0.005na/rtHz. Would you then come up with 3.3Mohms as meaning something?


YOU
>** Proves you have no real understanding of input noise.
>
> Just a plie of rote learned irrelevances.


Please go into this in greater detail. My understanding is that when using amplifiers, especially audio, the noise figure is a function of the
application - impedance levels, feeback and other external circuitry, closed loop gain setting. etc. Therefore NF is usually not specified on the data
sheet and instead the equivalent voltage and current densities at the input are specified, which allows the user to determine the added noise of the
amp or gain block Since the voltage noise density and current noise density are caused by different mechanisms, they are independent and are treated
separately and their results added by superposition. So, as shown before,

For the microphone preamp app previously given, using a typical microphone impedance of 150 ohms, and choosing a gain of 1000, then

mic noise amp input voltage noise amp input current noise
density density density

SSM (1.6 nV/rtHz) (1 nV/rtHz) (2pA/rtHz× 150 ohms)

OPA (1.6 nV/rtHz) (2.7 nV/rtHz) (1pA/rtHz x {150+10/(10+1000)}

total input noise density

SSM = sqrt{(1.6 nV/rtHz)^2 + (1 nV/rtHz)^2 + (2pA/rtHz× 150 ohms)^2} = 1.96nV/rtHz

OPA = sqrt{(1.6 nV/rtHz)^2 + (3.0 nV/rtHz)^2 + (1pA/rtHz x [150+10/(10+1000)]^2} = 3.0nv/rtHz

and over the audio band the total input referred noise is SSM = 0.28nV OPA = 0.43nV

I think these numbers give the user everything he needs to determine the noise levels and noise added by the amp. However, you say the user needs to
consider NF and you say 3.3Kohms is the best source resistor for best NF for the OPA and you arrived at that number by dividing the input voltage
noise density by the input current density. So,

Now I have a few questions. 1) please explain the physical significance of dividing the input noise density by the input current density.
2) please explain how the 3.3Kohm source resistor you arrive at by doing this improves the noise or any
other performance parameter. please show calculations showing lower numbers than those above
3) Since the SSM has a higher input noise current density and would therefore give a lower resistor for
this calculation, does this mean better amps have higher input noise current densities?
4) As mentioned earlier, if I use a Darlington follower on the OPA inputs and lower the input current
density to 5pa, would you now use a 3.3Mohm source resistor?

Since you are an expert and I am not, so you say, perhaps you can explain Ohm's Law to me. See, I always thought Ohm's Law stated that the voltage
across an impedance (resistance) was linearly proportional to the current through it, and the constant of proportionality was the value of the
resistance. Since the input noise voltage density is due thermal noise of the parasitic base resistance,and the input current noise density is due to
the shot noise of the collector divided by transistor beta, and the component due to base shot noise times base resistance is negligible in this case,
then the input noise voltage and current are independent and uncorrelated. I don't think Ohm's Law defines a resistor in the case of independent
values for voltage and current. I always thought they had to be linearly related to define a resistance.

Please try to answer in a mature way and support your position with technical calculations or references. Try to provide a technical discussion. If
you have some knowledge new to me, I'd like to learn it. See if you can avoid deleting large parts of posts you find inconvenient and resorting to
insults and name calling and stating over and over that you are an audio expert and I'm not.

However, I don't really expect to get a rational technical answer to the questions I've asked. I hope I'm surprised, but based on your past responses
in this and other threads, I'm getting a picture of how you click. Look at this below

> How sickening.


>> I said you had an attitude and often
>> called past posters idiots when they were looking for help.

>
>** And you're real sure they were not all idiots ?
>
> How would YOU know that?
>
> I doubt you have any way to tell.


Is this the way you live your life? Did you not get enough love when you were little?




 




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